1. Field of the Invention
The disclosures herein generally relate to an optical device and a light irradiation apparatus.
2. Description of the Related Art
Recently, intensive investigations have started on high-power lasers, for such as various kinds of optical instruments, laser projectors or light source lasers for laser processing machines. Such high-power lasers have achieved high output by focusing light from surface-emitting laser arrays, for example. A surface-emitting laser is suitable for a light source of a high-power laser according to a characteristic that light is emitted in a direction orthogonal to a substrate, a characteristic of easy integration and a characteristic of being easily testable. As a configuration of the high-power laser, for example, a configuration has been known in which a collimator lens including a microlens array is arranged in a light emission direction of a surface-emitting laser array which is a light source and furthermore a light focusing lens is arranged.
A surface-emitting laser array has a configuration, in which surface-emitting lasers each having mesa structures several tens of micrometers square as unit elements are arranged in a square lattice shape or in a hexagonal closed packed lattice shape. On the other hand, a microlens array for generating collimator light from the light emitted from the surface-emitting laser array is made of synthetic quartz or the like and is formed corresponding to the unit element of the surface-emitting laser array.
The surface-emitting laser array and the microlens array, as described above, require high mounting accuracy of ±tens of micrometers in three directions of X, Y and Z for mounting the microlens on the surface-emitting laser in order to improve utilization efficiency of light of the surface-emitting laser. Then, various investigations for improving accuracy of mounting a microlens on a surface-emitting laser have been performed. Specific examples in the related art of aligning a microlens with a surface-emitting laser with high accuracy are as follows:
The first example in the related art of aligning a microlens with a surface-emitting laser is a photonic device. The photonic device is a device in which the surface-emitting laser and the microlens are integrated. The photonic device has a microlens structure, in which plural leg portions are provided on a substrate on which the surface-emitting laser is formed in order to keep a predetermined distance from the surface-emitting laser.
In the photonic device, as described above, the leg portions, which are integrated with the microlens structure and are extended, are fixed on a surface of the substrate on which the surface-emitting laser is formed. In addition, for aligning in the XY-directions, two kinds of positioning methods, i.e. positioning while monitoring images of the surface-emitting laser and of the lens and positioning while causing the surface-emitting laser to emit light and receiving light having transmitted through the lens, are disclosed (See, for example, Japanese Published Patent Application No. 2007-142425).
The second example in the related art of aligning a microlens with a surface-emitting laser is an optical element mounting apparatus. In the optical element mounting apparatus, a protrusion of an alignment reference portion is integrally formed on one side of a microlens array substrate. Then, a depression of the alignment reference portion is integrally formed on one side of a surface-emitting laser array substrate, and both the alignment reference portions are fitted to each other. In this optical element mounting apparatus, mounting with high accuracy is required because a light emission unit of the surface-emitting laser and a microlens have structures corresponding one-to-one to each other.
In addition, in the above-described optical element mounting apparatus, the protrusion on the side of the microlens is formed integrally with the microlens upon resin molding of the microlens, and the depression on the substrate on the side of the surface-emitting laser array is manufactured by etching using a photolithography technology of a semiconductor process (See, for example, Japanese Published Patent Application No. 2004-288713).